1. Field of the Invention
The present invention relates to optical disc players that are suitable for playing back optical discs such as audio discs and/or video discs and, more particularly, to protection systems for optical disc players.
2. Description of Related Art
Recently, in the field of record disc equipments, digital audio disc and/or video disc playback systems utilizing pulse code modulation (PCM) technology to playback sound and/or video image as faithfully as possible have been developed. Of these systems, audio disc playback systems employing compact discs (trade name) and video disc playback systems employing laser discs (trade name) have become especially popular.
The compact disc (referred as CD hereafter), for example, conventionally used in a digital audio disc playback system is made from a transparent resin and has a diameter of approximately 12 cm and a thickness of approximately 1.2 mm. The CD has a thin metal film deposited on at least one disc surface, and pits or depressions are formed in the thin metal film. The pits of depressions produce light reflectivities that are different from the reflectivity of the non-pitted portions of the metal film and that correspond to 1 or 0 digitized data. The pits and the non-pitted portions are alternatively lined in a form of spiral or concentric pit train or track in the information storage area of the CD. When a signal is read out from a CD, the CD is rotated at a variable rotation speed between 200 and 500 rpm. An optical pickup incorporating a semiconductor laser or photoelectric transducing device traces the pit train or track of the rotating CD with constant linear velocity while moving radially from the center portions toward the outer portions.
A CD stores such a large quantity of information that a single side can provide approximately one hour of stereophonic music. A CD is far superior to a conventional analog phonograph record in sound quality, information storage density, and applicability to sophisticated control facilities.
Generally, CD, players have a precise machanical construction for playing back such a large quantity of information. Conventional CD players intended, for example, for home use and or portable outdoor use, however, do not possess sufficient mechanical durability to satisfy the demand for adequate operating flexibility and simplicity. For example, conventional CD players are provided with an optical pickup and a pickup actuator for moving the optical pickup radially in respect of a CD.
The pickup actuator is usually constructed in using a linear drive type motor comprised of a linear guide member, a moving member movable along the guide member and a stator member for driving the movable member. As is well known, in the linear motor the moving portion is controlled its movement by the stator portion in operating state of the motor. As a result, the position of the moving portion is controlled during the operating state of the motor. However, the moving member is free to move in the non-operating state of the motor. Therefore, optical pickups or pickup actuators must be locked mechanically for not moving during a transportion and/or a carriage of CD players. Otherwise the optical pickups or pickup actuators bump into guide ends due to exterior forces given in the transportion and/or the carriage so that they are damaged easily.
Optical pickups or pickup actuators, of course, are mechanically locked by manufacture or users prior to the transportion or the carriage to protect them from damage. However, there occur easily unlockings or incomplete lockings of optical pickups or pickup actuators by obilivion.